Electrophotographic apparatus

ABSTRACT

An electrophotographic apparatus including a developing station for developing an electrostatic charge pattern and a rotatable drum for moving a carrier having such a pattern thereon past the station. The developing station comprising a developing electrode at the station which is adjustable in relation to the path of the carrier and a developer feeder which supplies developer to the space between the electrode and the carrier for adherence to the charge zones of the pattern. The electrode adjusting apparatus providing for each lateral edge of the developing electrode to be adjusted independently of the other in its relation with the path of the carrier may be constituted of an electrode being pivotally mounted on a shaft which extends across the path of the carrier, is parallel thereto, and is at right angles to the direction of movement of the carrier. The electrode is provided with a projection which extends beyond the respective side of the path of the carrier, each projection having an internally threaded bore therethrough for receiving an adjusting screw which contacts a stop forming a portion of the housing. The electrode adjusting apparatus may also be constituted of an electrode being pivoted or axially displaced by at least one spacing element which contacts and moves over the surface of the carrier.

United States Patent [191 Gunder 1 1 ELECTROPHOTOGRAPHIC APPARATUS [75]Inventor: Klaus Gunder, Darmstadt, Germany [73] Assignee: HoechstAktiengesellschatt,

Wiesbaden-Biebrich, Germany 22 Filed: Dec. 21, 1972 [21] App]. No.:317,123

[30] Foreign Application Priority Data Dec. 24, 1971 Germany 2164494Oct. 16, 1972 Germany 2250703 [52] US. Cl. 118/637 [51] Int. Cl. G03G13/00 [58] Field of Search 117/175; 118/2, 6, 637; 355/3 DD, 14;lOl/DlG. 13

[56] References Cited UNITED STATES PATENTS 2,952,241 9/1960 Clark et a1118/637 3,011,474 12/1961 Ulrich 1. 118/637 3,105,426 10/1963 Bickmoreet al.... 355/3 DD 3,147,147 9/1964 Carlson 118/637 3,357,399 12/1967Fisher.,,. 118/637 3,416,494 12/1968 Hudson 118/637 3,662,711 5/1972Hudson 118/637 Primary ExaminerMorris Kaplan Attorney, Agent, orFirmStevens, Davis, Miller & Mosher 1 Aug. 5, 1975 5 7 ABSTRACT Anelectrophotographic apparatus including a developing station fordeveloping an electrostatic charge pattern and a rotatable drum formoving a carrier having such a pattern thereon past the station. Thedeveloping station comprising a developing electrode at the stationwhich is adjustable in relation to the path of the carrier and adeveloper feeder which supplies developer to the space between theelectrode and the carrier for adherence to the charge zones of thepattern. The electrode adjusting apparatus providing for each lateraledge of the developing electrode to be adjusted independently of theother in its relation with the path of the carrier may be constituted ofan electrode being pivotally mounted on a shaft which ex tends acrossthe path of the carrier, is parallel thereto. and is at right angles tothe direction of movement of the carrier. The electrode is provided witha projection which extends beyond the respective side of the path of thecarrier, each projection having an internally threaded bore therethroughfor receiving an adjusting screw which contacts a stop forming a portionof the housing. The electrode adjusting apparatus may also beconstituted of an electrode being pivoted or axially displaced by atleast one spacing element which contacts and moves over the surface ofthe carrier.

8 Claims, 7 Drawing Figures SHEET PATENTED 51975 SHEET PATENTEU 5W5 Q onmm R w 0 m wN W 3 ELECTROPHOTOGRAPHIC APPARATUS The present inventionrelates to electrophotographic apparatus.

Electrostatic charge patterns are widely produced nowadays, especiallyin electrophotographic reproduction machines, and may be renderedvisible with, for example, the aid of a two-component developer. In adeveloping process of this kind, color-producing components of thedeveloper are preferentially deposited at the zones where thedifferences in charge are greatest and in some cases it is difficult todevelop grey tones and larger dark areas. Thus, for example, the largeareas are usually developed only at the edges, remaining bright in themiddle. Attempts have been made to overcome these difficulties by theuse of so-called developing electrodes.

The use of developing electrodes, however, causes numerous otherdifficulties. Thus, for example, it is particularly difficult to keepthe field distribution produced by a developing electrode constant inthe case of a relatively wide photoconductor. Furthermore, whenphotoconductor drums are changed in electrophotographic reproductionmachines, there is a danger that the geometric arrangement will nolonger be exact and that development will take place unevenly over thewidth of the imagev The present invention provides electrophotographicapparatus which comprises a developing station for de veloping anelectrostatic charge pattern and means for moving a carrier having sucha pattern thereon over a predetermined path past the station, thestation comprising a developing electrode which can be connected to avoltage source and beneath which the pattern can be developed by meansofa developer of which at least a part adheres to the charged zones ofthe pattern, the position of the developing electrode in relation to thepath of the carrier being adjustable.

The present invention makes it possible to obtain good development overthe entire surface and good development of grey tones. These goodresults can be obtained over long periods, and even when the materialcarrying the charge pattern (the carrier) is changed.

More particularly, the adjustable arrangement of the developingelectrode enables problems relating to the fitting of the electrode tobe solved and allows account to be taken of variations in dimensionsoccurring during manufacture of the electrodes. It is also possible byvarying the adjustment to obtain different qualities of copy and, forexample, to set the apparatus to suit particular originals, for examplethose exhibiting slight contrast. Finally, it may also be possible touse a slightly twisted developing electrode without the quality of thecopy suffering, by adjusting the position of the electrode to compensatefor the twist,

In the simplest case the developing electrode is secured in the copyingmachine with the aid of adjusting means permitting fine adjustment ofthe position of the electrode in relation to the path of travel of therecord carrier. The adjusting means are preferably so designed andarranged in the copying machine that the distances of the two lateraledges of the developing electrode from the path of the record carriercan be adjusted independently of each other. By means of thisarrangement, the distance between the developing electrode and the pathof the record carrier can be adjusted, and

unintentional inclination of the electrode relative to the path of thecarrier can be corrected.

In the embodiment of the present invention described above thedeveloping electrode is preferably pivotally mounted on a shaft whichextends across the path of the carrier, is parallel thereto, and is atright angles to the direction of movement of the carrier. Each lateraledge of the developing electrode is advantageously provided with aprojection which extends beyond the respective side of the path of thecarrier, each projection having an internally threaded bore therethroughfor receiving an adjusting screw and the housing of the apparatuscomprising a stop for the end of each adjusting screw. The apparatus mayalso comprise locking means for securing the adjusting means againstunintended movement. The locking means advantageously comprises twoscrews, one positioned on each side of the path of the carrier, eachscrew passing through a respective bore in the developing electrode andbeing received in a respective internally threaded recess in the housingof the apparatus.

According to the present invention, for all those cases in which a rigidarrangement of the developing electrode is not required, the electrodeis so formed and arranged in the apparatus that it is in mechanicalengagement with a support for the record material, so that the distancebetween the developing electrode and the carrier of the electrostaticpattern and their position relative to each other are automatically keptconstant. Accordingly, the apparatus of the present invention may,instead of comprising the adjusting means described above, comprisesupport means for moving the carrier and determining its path past thedeveloping electrode, the developing electrode being such that it can bepivoted and/or axially displaced and being provided with at least onedistance piece which can contact, and move over, the surface of thesupport.

The developing electrode may be pivotally mounted on a shaft whichextends across the path of the carrier, is parallel thereto, and is atright angles to the direction of movement of the carrier, the shaftbeing positioned either upstream or downstream of the zone in whichdeveloping takes place; in this case, a distance piece is preferablyprovided at each lateral edge of the developing electrode.

Alternatively, the developing electrode may be pivotally mounted on ashaft which extends across the path of the carrier above the zone inwhich developing takes place, the shaft being parallel to the carrier atright angles to its direction of movement. In this case, the developingelectrode is such that it can be moved along a line at right angles tothe portion of the carrier located beneath the shaft and there are atleast two distance pieces, the two lateral edges, and the leading andtrailing edges, of the developing electrode each being provided with atleast one distance piece. If there are only two distance pieces theseare disposed at diametri cally opposite corners of the developingelectrode, Preferably, however, there are four distance pieces arrangedat the corners of a square or rectangle, one distance piece beingdisposed at each corner of the developing electrode. In a preferred formof the abovedescribed apparatus, each end of the shaft projects througha slot in the shaft mounting, the slot extending at right angles to thesurface of the support,

The distance piece or each distance piece in the ap paratus of theinvention is advantageously biased against the surface of the support.Each distance piece preferably comprises a roller mounted on a spindlewhich is parallel to the carrier and is at right angles to its directionof movement.

In the apparatus of the present invention, the support means preferablycomprises a drum and the carrier 3 photoconductor. The drum may includea lock for the photoconductor. If it does, the surface of the drumpreferably has a raised portion of such a length that it subtendssubstantially the same angle at the center of the drum as does thedeveloping zone, the raised portion being so disposed in relation to thelock that it remains in contact with the distance piece(s) as long asthe lock is moving beneath the developing electrode. and the amount bywhich the raised portion extends beyond the surface of the drum being atleast equal to the amount by which the lock projects beyond the surfaceof the drum.

The position of the developing electrode can also be controlled byhydraulic or electromagnetic means.

In the developing zone, the developing electrode preferably has a brightsurface finish. It may be made of aluminum.

The apparatus may also comprise guide means for dividing the developerinto two partial streams of different sizes, the smaller partial streampassing between the developing electrode and the carrier and the largerpartial stream contacting the portion of the carrier that has passedbeneath the developing electrode. The amount of developer that flowsbeneath the developing electrode is preferably 2 to 12%, advantageouslyof the total amount of developer. The apparatus advantageously alsocomprises a cascade feed device for supplying developer to thedeveloping zone, a reservoir for developer being provided upstream ofthe developing zone and the magnitude of the smaller partial streambeing determined only by the movement of the carrier and the developingelectrode.

The particular advantages of the non-rigid apparatus of the presentinvention are as follows. As a result of the self-adjustment of thedistance between the developing electrode and the photoconductor(carrier), a single setting of the guide means for the electrodesuffices, so that the desired conditions are maintained even when thephotoconductor or its drum is changed, or when other maintenanceoperations are carried out. Damage to the developing electrode and inparticular to its polished surface is prevented. The apparatus can beincorporated in electrophotographic reproduction machines without highcosts being incurred.

The present invention will now be described, by way of example only,with reference to the accompanying drawings, in which:

FIG. I is a diagrammatic representation of an electrophotographicreproduction machine;

FIG. 2a is a diagrammatic representation of a developing electrode;

FIG. 2b is a side elevational view of the electrode of FIG. 22;

FIG. 3 shows a developing electrode and a photoconductor drum withcontrol surfaces and distance pieces;

FIG. 4 shows yet another form of developing electrode;

FIG. 5 illustrates a form of construction of the apparatus of theinvention comprising a fixed but adjustable arrangement for setting theposition of the developing electrode; and

FIG. 6 is a front elevation view of the apparatus of FIG. 5.

Referring now to FIG. I of the drawings, a photoconductor 2, fitted on adrum 1, can be charged uniformly by a corona-discharge unit 3. Thecharged photoconductor 2 can be exposed to provide an image at anexposure station 4, and can be developed in a developing station 5, thelatter comprising two zones. The developed charge pattern can betransferred in the transfer station 6 to a copy carrier 7, for example,paper. The apparatus of the invention can of course also be used if zincoxide paper (ZnO paper) is employed instead of a photoconductor 2 thatcan be repeatedly used. In this case there is of course no transferstation 6, since the zinc oxide paper constitutes the photoconductor andthe material for carrying the copy.

Developing of the electrostatic charge pattern produced in the exposurestation 4 takes place in the following manner. Developer 10 is passedfrom a supply container 8 with the aid of a bucket conveyor system 9 andis allowed to trickle over a developing electrode II. Part of thedeveloper I0 passes into the reservoir 12 from which it is carriedbeneath the developing electrode II by the photoconductor 2. The mainmass of the developer 10, however, flows past the outer face of theelectrode 11 and trickles over that zone of the photoconductor 2 thathas been previously developed below the developing electrode 11. Thedeveloping electrode II has a projection 13, the purpose of which is tocontrol the quantity of developer that can pass below the actualdeveloping zone b c of the electrode 11.

The distance between the electrode 11 and the photoconductor 2 at thepoint c is approximately 2.4 mm and at the point b about 1.6 mm. In someof the Figures these distances are not shown to scale in order to renderthe Figures in question clearer. The mean thickness of the carriermaterial is approximately 0.4 mm.

Since the distance between the electrode II and the photoconductor inthe developing zone c b is extremely critical, the electrode 11 ismounted to pivot about spindle 14 (see FIG. 2b). To enable the electrode1 1 always to remain at the same constant distance from the carrier 2 ofthe electrostatic charge pattern, freely rotatable and preferablyinsulated rollers or small wheels 15 are fitted at its sides, and thesecan run on the surface of the photoconductor or on the surface of thedrum (see FIG. 2a). The developing electrode 11 may be pressed againstthe photoconductor drum 1 by a spring 16 (See FIG. 2b). The spindles 14on which the developing electrode 11 can pivot are mounted to rotate inarms 17.

It has been found that with the aid of a single setting of the arms 17in the above-described apparatus, copies of uniformly high quality canalways be obtained without, for example. the changing of thephotoconductor or of the drum therefor resulting in any trouble.

A modified form of photoconductor drum which can be used in theapparatus of the present invention is il lustrated in FIG. 3. To securethe photoconductor 2 on the drum 1 and at the same time to preventpenetration of developer into the interior of the drum, there isprovided a lock 18 which extends over the entire width of the strip ofphotoconductive material 2. This lock 18 is not precisely flush with thesurface of the drum 1, but for the most part projects slightly abovesaid surface. The present invention makes it possible to ensure that thedeveloping electrode 11 is not permanently displaced from its setposition or damaged by the projecting lock 18. For this purpose, aprojection 19 is provided at each side of the photoconductor 2 and overan angular zone a which corresponds to the actual developing zone of theelectrode. that is, to the angle between b and c. Each of theseprojections 19 projects beyond the surface of the drum to an extent atleast equal to the extent by which the lock 18 projects beyond thesurface of the drum.

The projections 19 are so arranged, that when the drum 1 is turning,they move into contact with the rollers when the lock 18 moves below thedeveloping electrode 11. The electrode I1 is lifted from the surface ofthe drum by the projections and the lock 18 does not come into contactwith it. When the lock 18 has passed below the electrode 11, the wheels15 roll over the rearward end of the projection 19, and the electrode 11is again brought into the original spaced relationship with thephotoconductor 2. This arrangement offers the particular advantage thatthe lock 18 can be of relatively uncomplicated construction without itbeing necessary to forego the use of an electrode 11 that lies close tothe photoconductor 2.

A further embodiment of the apparatus of the invention is illustrated inFIG. 4. In this example the developing electrode 11 is not only adaptedto swing about a spindle 14 but is also movable perpendicularly as awhole towards and away from the photoconductor 2. For this purpose arms37 are each provided with a slot 20 in which the spindle 14 can move. Inthis embodiment, the developing electrode 11 has two wheels 15, and twowheels 15', only two of which are shown in FIG. 4.

The developing electrode 11 is pressed against the photoconductor drum 1by springs 21 and 21 which are compressed between the electrode and abacking element 22 mounted on the arms 17. This arrangement offers theadditional advantage that even if the photoconductor drum 1 ispositioned off-center, this has no effect on the conditions of thedeveloping process. The developing electrode 11 always remains in thesame specific position in relation to the photoconductor drum 1, Le, italways remains at the desired distance from the drum.

In the case of the embodiment of the present inven tion illustrated inFIGS. 5 and 6, the position of the developing electrode is not adjustedautomatically in the manner described with reference to FIGS. 1 to 4;instead. the apparatus is provided with an adjusting unit to which thedeveloping electrode is secured.

In the apparatus shown in FIGS. 5 and 6, the distance between thedeveloping electrode 11 and the photo conductor 2 is about 2 mm. Themean thickness of the carrier material is about 0.4 mm. In general, adistance between the electrode 11 and the charge pattern that isapproximately 4 to 6 times as great as the mean thickness of the carrieris preferred. The electrode 11 has a projection 13 which serves thepurpose of measuring out the quantity of developer passing below theactual electrode. To vary the quality of the copies and in particular toeliminate a poor quality of copy, the developing electrode 11 isconnected to an adjusting device.

The electrode 11 is firmly connected to two U- section bars 24 mountedon either side of the electrode. These bars 24 are mounted with the aidof bearings 25 on shafts 26 in retaining elements 27 which are firmlyconnected to the housing of the copying machine.

Projections 28 extend outwards from the U-section bars 24, theseprojections each having a fine female screw-thread 29. Cooperating withthe screw-threads 29 are screws 30 the ends of which bear againstbacking elements 31 which are firmly connected to the retaining elements27. By turning the screws 30 the dis tance of the developing electrodeII from the photoconductor 2 can be adjusted independently at each side.

To avoid unintentional displacement of the finethreaded screws 30, thereare provided counter-screws 32. These counter-screws cooperate withscrewthreads 33 in the retaining elements 27 and extend through bores 34in the U-section bars 24. Tightening of the counter-screws 32 after theadjusting screws 30 have been set causes a pressure to be exerted on thefine screw-threads and this is sufficient to prevent the screws 30 frombeing unintentionally turned.

The longitudinal axes of the adjusting screws 30 and also of thecounter-screws 32 do not intersect the shafts 26. This is necessary inorder to enable the position of the developing electrode 11 to beadjusted by its being swung about the shafts 26 and to enable theelectrode 11 to be locked in position.

What is claimed is:

1. Electrophotographic apparatus which comprises a developing stationfor developing an electrostatic charge pattern and means for moving acarrier having such a pattern thereon over a predetermined path past thestation, the station comprising a developing electrode which can beconnected to a voltage source and beneath which the pattern can bedeveloped by means of a developer of which at least a part adheres tothe charged zones of the pattern, the position of said developingelectrode in relation to the path of the carrier being adjustable, saiddeveloping electrode being pivotally mounted on a shaft which extendsacross the path of the carrier, is parallel to said shaft, is at rightangles to the direction of movement of the carrier, and is connected totwo bars mounted on either side of the developing electrode, each barbeing provided with a projection which extends outwards from the bar andbeyond the respective side of the path of the carrier, each projectionhaving an internally threaded bore therethrough for receiving anadjusting screw and the housing of the apparatus comprising a stop forthe end of each adjusting screw.

2. The apparatus of claim 1 also comprising locking means for securingthe adjusting means against unin tended movement.

3. The apparatus of claim 2 wherein the locking means comprises twoscrews, one positioned on each side of the path of the carrier, eachscrew passing through a respective bore in the developing electrode andbeing received in a respective internally threaded recess in the housingof the apparatus.

4. The apparatus of claim I wherein the means for moving the carrier anddetermining its path comprises a rotatable drum.

5. The apparatus of claim 1 also comprising guide means for dividing thedeveloper into two partial streams of different sizes, the smallerpartial stream passing between the developing electrode and the carrierand the larger partial stream contacting the portion oping zone, areservoir for developer being provided upstream of the developing zoneand the magnitude of the smaller partial stream being determined only bythe movement of the carrier and the developing electrode.

8. The apparatus of claim 1 wherein the developing electrode has abright surface in the developing zone. 1K

1. Electrophotographic apparatus which comprises a developing stationfor developing an electrostatic charge pattern and means for moving acarrier having such a pattern thereon over a predetermined path past thestation, the station comprising a developing electrode which can beconnected to a voltage source and beneath which the pattern can bedeveloped by means of a developer of which at least a part adheres tothe charged zones of the pattern, the position of said developingelectrode in relation to the path of the carrier being adjustable, saiddeveloping electrode being pivotally mounted on a shaft which extendsacross the path of the carrier, is parallel to said shaft, is at rightangles to the direction of movement of the carrier, and is connected totwo bars mounted on either side of the developing electrode, each barbeing provided with a projection which extends outwards from the bar andbeyond the respective side of the path of the carrier, each projectionhaving an internally threaded bore therethrough for receiving anadjusting screw and the housing of the apparatus comprising a stop forthe end of each adjusting screw.
 2. The apparatus of claim 1 alsocomprising locking means for securing the adjusting means againstunintended movement.
 3. The apparatus of claim 2 wherein the lockingmeans comprises two screws, one positioned on each side of the path ofthe carrier, each screw passing through a respective bore in thedeveloping electrode and being received in a respective internallythreaded recess in the housing of the apparatus.
 4. The apparatus ofclaim 1 wherein the means for moving the carrier and determining itspath comprises a rotatable drum.
 5. The apparatus of claim 1 alsocomprising guide means for dividing the developer into two partialstreams of different sizes, the smaller partial stream passing betweenthe developing electrode and the carrier and the larger partial streamcontacting the portion of the carrier that has passed beneath thedeveloping electrode.
 6. The apparatus of claim 5 wherein the smallerpartial stream comprises from 2 to 12% of the total amount of developer.7. The apparatus of claim 5 also comprising a cascade feed device forsupplying developer to the developing zone, a reservoir for developerbeing provided upstream of the developing zone and the magnitude of thesmaller partial stream being determined only by the movement of thecarrier and the developing electrode.
 8. The apparatus of claim 1wherein the developing electrode has a bright surface in the developingzone.